Method of determining the utility of carbons for depolarizing electrodes



Feb. 20, 1940. w. WISFELD 2,190,317

um'mdb or DETERMINING was UTILITYOF masons FOR wromaxzm ELEC'IRQDES w FiladDec. 4, 1936 Patented Feb. 20, 1940 UNITED STATES PATENT OFFICE METHOfi F DETERMINING THE UTILITY. OF

CARBONS FOR DEPOLARIZING ELEC- TRODES Application December 4, 1936, Serial No. 114,258

2 claims. (01. 136-121) This invention relates toa positive electrode for galvanic cells. i Active carbon has recently been largely use as eiIective depolarising composition for the production of positive electrodes for galvanic cells, suchelectrodes being constituted entirely, or only partially, of such carbon. Practical experience with galvanic cells in which active carbon has been employed as depolariser, has now shown that the behaviour of active carbons employed for this purpose varies considerably. Thus, carbone of equal capacity in respect of adsorptionwhich is a factor usually accepted as a criterion of their value-do not display any concordance in behaviour as depolarisers.

It has been established in accordance with the present invention that the suitability of active carbons for depolarising increases with their power of decomposing a solution of hydrogen 2g peroxide. It has been ascertained that active carbons are extremely suitable as depolarisers if they are so constituted that 0.2 grrn. of the .pulverised carbon, suspended in 10 cc. of distilled water in a heat-insulated vessel, and treated with u 25 cc. of a 3% solution of hydrogen peroxide, cause the temperature (initially C.) of the mixture to rise by at least 1 C. within 3 minutes. or eifect the liberation of at least cc. of oxygen (measured at 0 C. and 760 mm. Hg). This test does not involve either oxidation or reduction. It is a decomposition of hydrogen peroxide by the catalytic action of the carbon according to the equation .2HzOz=2H2O+Oz. This reaction is definitely exothermic as is generally true of the a decomposition of peroxides, and liberates a substantial quantity of heat.

The oxygen is not absorbed by the carbon and then driven ofi, but is liberated directly into the atmosphere.

In order more clearly to understand the invention, reference is made to the accompanying drawing, in which Figs. 1 and 2 are curve diagrams showing relative behaviour of three kinds of active carbon of equal adsorption capacity, towards hydrogen peroxide. In Fig. 1 the abscissa are plotted as seconds and the ordinates as degrees centigrade. In Fig. 2 the abscissa are plotted in hours and the ordinates in volts. The

curve A in Fig. 1 represents the behaviour of a carbon that is specially suitable for galvanic cells,

whilst curve B relates to an active carbon that is still suitable for that purpose. The carbon of larly suitable as depolariser, reveals a considerable rise of temperature per unit of time, viz.

' from 20 C. to about 24 C.- in the first minute,

to about 27 C. in the second minute and to about 29" C. in the third minute. The temperature rise shown by the curve is in direct proportion to the rate at which the hydrogen peroxide is decomposed by the carbon, the liberation of oxygen under the same conditions amounting to 125 .cc. The curve B indicates a smaller rise in temperature-in this case from 20 C. to about 21.7" C. at the end of the third minute, the

amount of oxygen disengaged being 32 cc. As already stated, this carbon is just still employable as depolariser. In the case of curve C, the carbon unsuitable for the purpose in view shows a temperature rise of less than 1 C. at the end of the third minute, and the amount of oxygen liberated during that period is 12 cc.

The curves in Fig. 2 graphically reproduce the behaviour of the carbons--the reaction curves of which are represented in Fig. lin cells of identical construction, and illustrate their relative efficiency as regards the progressive voltage drop during continuous discharging oi the cells under identical loading conditions. As is manifest, the efliciency curves of Fig. 2 are fully concordant with those of Fig. l.

Moreover, these observations are not restricted to the behaviour of activecarbons as depolarlsers in atmospheric oxygen cells, but it was ascertained, in further developing the invention, that the aforesaid experiences on the differences exhibited by, otherwise equivalent. active carbons decomposing hydrogen peroxide solutions corresponds to the characteristic specified.

Example The following represents a comparison between two peat cokes, prepared in the same manner. with regard to their power of decomposing bydrogen peroxide, and their behaviour in an atmospheric oxygen cell.

The cokes possessed the same adsorptive capacities as measured by a methylene blue solution. In both cases 9 cc. of a solution of 1.5 gm.

of methylene blue in 1000 cc. of distilled water I was decolorized by 0.1 gm; of the pulverized coke.

a 0.1 grm. of the finely powdered peat coke was suspended in 5 cc. of distilled waterandtreatedwith 10 cc. of 3% solution of hydrogen peroxide,

the amount of oxygen liberated within 1 minute being then measured. The material A'liberated 18 cc. of oxygen, whilst the'material B efiected the separation of less than 2 cc. of oxygen.

The two products differ in a similarmanner as regards their behaviour when employed as elec- '-trode material in a galvanic cell withatmospheric-oxygen depolarisation. The cell equipped with the product A showed a terminal voltage of 1.42 volts andduring discharge througha constant resistance-a mean discharge voltage of 1.1 volts. On the other hand, the cell fitted with the material B gave a terminal voltage of only 1.26 volts and-under the same loading conditions as in the case of product Aa mean dis charge voltage of 0.85 volt.

I claim: V

1. A method oi'determining the utility of ac tive carbons for use as depolarizing agents in t1". positive electrodes of air depolarized galvani cells which comprises mixing the active carbor in finely divided form with aqueous solutions c hydrogen peroxide, measuring the rise in tem perature of the solution to determine those ac tive carbons which give a rise in temperature at least 1 C. when 0.2 gram of the carbon sus pended in 10 cc. of distilled water are mixed wit 25 cc. of a 3% solution of hydrogen peroxide 2 2.A methodof determining the utility of ac tive-carbons for use as depolarizing agents in th positive electrodes of air depolarized galvani cells which comprises mixing the active carbon in finely divided form with aqueous solutions c hydrogen peroxide, measuring the quantity c oxygen liberated therefrom to determine thos active carbons which liberate at least 25 cc. 0 oxygen within 3 minutes when0.2 gram of th carbon suspended in- 10 cc. of distilled water ar mixed with 2500. of a 3% solution of hydroge: peroxide at 20 C.

l WERNER WISFELD. 

